1. Field of the Invention
The present invention relates to a video signal processor equipped with a copy preventive function and capable of executing on/off control of such a copy preventive function.
2. Description of the Related Art
In a conventional video apparatus such as analog VTRs known heretofore, it has been customary that in the manufacture of soft tape a disturbance signal adapted to disturb the operation of an AGC circuit in a recording section of the VTR is inserted, for the purpose of protecting a copyright, on a predetermined line during a vertical blanking interval of a video signal. Due to the existence of such a disturbance signal, if the soft tape is illegally dubbed by any third person, the dubbed tape is rendered in a non-reproducible state to consequently achieve desired protection of the copyright. There is a known U.S. Pat. No. 4,631,603 regarding to this protection.
Meanwhile, wide progress has been observed of late in digital video apparatus with resultant remarkable improvements in picture quality. Since video signals in digital video apparatus are essentially superior in quality, it is demanded more often than analog video apparatuses and therefore it is desirable that an adequate circuit be incorporated to inhibit both digital-to-digital dubbing and digital-to-analog dubbing. Video compression technology for limiting the quantity of data is adopted in digital video apparatus currently available, particularly in digital VTRs and some apparatus designed to deal with digital television broadcasting, video-CD, CDI, video karaoke and so forth which have a signal format conforming with the MPEG (Motion Picture Experts Group) standard. Generally the digital video signal processed in such apparatus is composed merely of data representing the actual picture itself, and signal components relative to vertical blanking, horizontal blanking and so forth not directly related to the picture are eliminated.
Normally, each of the digital video apparatus incorporates a video signal processor therein to convert a digital video signal into an ordinary analog television signal having data of blanking intervals. Under such circumstances, there recently has been an idea to insert, in the video signal processor, the aforementioned disturbance signal into a vertical blanking interval to thereby substantially inhibit the recording, on any tape, of the analog television signal outputted from the video apparatus.
European Patent application number 0580367 published on Jan. 26, 1994, discloses a copy protection system. Unpublished Japanese patent application number 05277633 and 06040450 discloses a similar copy protection video system. Each of the above applications are owned by the assignee of the present invention and corresponding U.S. applications are still pending.
Although the above-described inhibition of any illegal video recording on tape is very much in demand, it is also desired on the other hand that the video-recording inhibited state be canceled to permit a condition where the television signal from the video apparatus is recordable on tape when properly in compliance with requirements inherent to the video apparatus. In other words, it is also desired that on/off control of the copy inhibiting process be executable freely.
One specific method for realizing such on/off control of the copy inhibiting process in the aforementioned video signal processor, may be to allocate on/off control data of 1 bit to each register. However, in employing this method, it is possible for a third person to easily find which bit in a bit stream is used for on/off control of the copy inhibiting process by monitoring and comparing the bit stream at the on-time and at the off-time of the copy inhibiting process by means of a logic analyzer or the like. Accordingly, there arises a problem that the copy inhibiting process can be illegally canceled by a third person. And even if a command for on/off control of the copy inhibiting process is composed of a plurality of bits, it is still possible to cancel the copy inhibiting process with facility in the same manner as described above.